[ 
https://issues.apache.org/jira/browse/HDFS-16182?focusedWorklogId=640600&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-640600
 ]

ASF GitHub Bot logged work on HDFS-16182:
-----------------------------------------

                Author: ASF GitHub Bot
            Created on: 23/Aug/21 07:30
            Start Date: 23/Aug/21 07:30
    Worklog Time Spent: 10m 
      Work Description: Neilxzn opened a new pull request #3320:
URL: https://github.com/apache/hadoop/pull/3320


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   ### Description of PR
   https://issues.apache.org/jira/browse/HDFS-16182
   
   ### How was this patch tested?
   add  TestBlockStoragePolicy.testAddDatanode2ExistingPipelineInSsd
   
   ### For code changes:
   
   - [ ] Does the title or this PR starts with the corresponding JIRA issue id 
(e.g. 'HADOOP-17799. Your PR title ...')?
   - [ ] Object storage: have the integration tests been executed and the 
endpoint declared according to the connector-specific documentation?
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Issue Time Tracking
-------------------

            Worklog Id:     (was: 640600)
    Remaining Estimate: 0h
            Time Spent: 10m

> numOfReplicas is given the wrong value in  
> BlockPlacementPolicyDefault$chooseTarget can cause DataStreamer to fail with 
> Heterogeneous Storage  
> -----------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-16182
>                 URL: https://issues.apache.org/jira/browse/HDFS-16182
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namanode
>    Affects Versions: 3.4.0
>            Reporter: Max  Xie
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> In our hdfs cluster, we use heterogeneous storage to store data in SSD  for a 
> better performance. Sometimes  hdfs client transfer data in pipline,  it will 
> throw IOException and exit.  Exception logs are below: 
> ```
> java.io.IOException: Failed to replace a bad datanode on the existing 
> pipeline due to no more good datanodes being available to try. (Nodes: 
> current=[DatanodeInfoWithStorage[dn01_ip:5004,DS-ef7882e0-427d-4c1e-b9ba-a929fac44fb4,DISK],
>  
> DatanodeInfoWithStorage[dn02_ip:5004,DS-3871282a-ad45-4332-866a-f000f9361ecb,DISK],
>  
> DatanodeInfoWithStorage[dn03_ip:5004,DS-a388c067-76a4-4014-a16c-ccc49c8da77b,SSD],
>  
> DatanodeInfoWithStorage[dn04_ip:5004,DS-b81da262-0dd9-4567-a498-c516fab84fe0,SSD],
>  
> DatanodeInfoWithStorage[dn05_ip:5004,DS-34e3af2e-da80-46ac-938c-6a3218a646b9,SSD]],
>  
> original=[DatanodeInfoWithStorage[dn01_ip:5004,DS-ef7882e0-427d-4c1e-b9ba-a929fac44fb4,DISK],
>  
> DatanodeInfoWithStorage[dn02_ip:5004,DS-3871282a-ad45-4332-866a-f000f9361ecb,DISK]]).
>  The current failed datanode replacement policy is DEFAULT, and a client may 
> configure this via 
> 'dfs.client.block.write.replace-datanode-on-failure.policy' in its 
> configuration.
> ```
> After search it,   I found when existing pipline need replace new dn to 
> transfer data, the client will get one additional dn from namenode  and check 
> that the number of dn is the original number + 1.
> ```
> ## DataStreamer$findNewDatanode
> if (nodes.length != original.length + 1) {
>  throw new IOException(
>  "Failed to replace a bad datanode on the existing pipeline "
>  + "due to no more good datanodes being available to try. "
>  + "(Nodes: current=" + Arrays.asList(nodes)
>  + ", original=" + Arrays.asList(original) + "). "
>  + "The current failed datanode replacement policy is "
>  + dfsClient.dtpReplaceDatanodeOnFailure
>  + ", and a client may configure this via '"
>  + BlockWrite.ReplaceDatanodeOnFailure.POLICY_KEY
>  + "' in its configuration.");
> }
> ```
> The root cause is that Namenode$getAdditionalDatanode returns multi datanodes 
> , not one in DataStreamer.addDatanode2ExistingPipeline. 
>  
> Maybe we can fix it in BlockPlacementPolicyDefault$chooseTarget.  I think 
> numOfReplicas should not be assigned by requiredStorageTypes.
>  
>    
>  
>  
>  
>  



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